Erewhon is a brand of U.S. Mills. The Erewhon company was actually founded in 1966 ("by two macrobiotic educators" according to U.S. Mills' website). In 1986, it was Erewhon that acquired U.S. Mills (the makers of Skinner's Raisin Bran and Uncle Same Cereals). The joint company chose to continue operations under the U.S. Mills' name.
For more about Erewhon, visit their official website.